I thought I'd let everyone know about a plugin we wrote 2 years ago but forgot to release until today
This is a simple plugin that lets you take over the unauthorised/login process for single content items or whole areas of the site. You can use this to do things like have a payment form to enter a private area, or, as we recently did, have a special login process for an extranet involving integration with a legacy system that gets a security token via async, all TTW (using plomino).
or you can just use it to have some more text on a normal login page.
Once installed it's simple to configure using content rules. Create a rule, tell it which page to redirect to and then apply it to the parts of the site you want.